A fly-ash monitor measures the percentage carbon (% C) in samples of fly ash. The fly ash is produced by combustion of pulverised coal in a coal-burning power station. The fly-ash samples are automatically collected from a duct. Most power stations have several ducts of this type such that several monitors will normally be required.
A known form of monitor receives the fly ash in a sample tube housed within a detector chamber which utilises microwave radiation in a resonance cavity to determine the % C. The chamber is heated at an elevated operating temperature to prevent moisture content of the ash causing coagulation of the ash within the tube. A mesh filter is provided at a base of the tube to provide a seat, upon which the ash is collected. After testing, the ash is purged from the tube by a charge of air which is jetted through the mesh filter. Such a monitor has proven unreliable at times, presumably as a result of any of a number of possible causes such as contaminating material falling back into the tube after purging, ash blocking the filter to prevent complete purging and/or the air temperature of the purged air dropping below the operating temperature such that the ash sticks inside the sample tube.